Koi Pond Water Quality

The number one requirement your koi fish need is clean, oxygenated water that is free from toxins. There is a saying that we are not just koi keepers, but water quality keepers. If the koi pond water contains toxins such as high ammonia, nitrite, and pH, the koi will not do well and may even perish. Maintaining clean water is not difficult, but it takes effort to ensure your water quality is balanced and healthy for your koi.

We are not just koi keepers, but water quality keepers.

– Rosimeri Tran

Testing Your Koi Pond Water Quality

So, how do you ensure good water quality for koi fish? The key components that you should be monitoring and testing to help your koi fish have good water quality are levels of ammonia, pH, nitrite, nitrate, and GH/KH.

To monitor your water quality, you will need two important tools.

  • Start with pond water test kits, usually found online or at pond supply stores. We use the API Fresh Water Master test kit, which contains test solutions for ammonia, pH, nitrite, and nitrate. Purchase a GH & KH test kit separately.
  • You should have a water thermometer such as those sold at pool stores. Monitoring your water temperature is important, especially when feeding the koi or treating your pond water.

Now that you have the tools needed to test the koi pond water, let us discuss each item to monitor and what can happen if unchecked.

Ammonia Levels

Ammonia is created from fish excreting their waste. A proper biological filtration system should be able to handle fish waste through the biological nitro cycle that occurs in most ponds. But overfeeding, overcrowding, and not doing weekly water changes can cause an ammonia spike. If ammonia levels in your koi pond go unchecked, it can be deadly to the koi. Signs of high ammonia are when koi become lethargic, they won’t eat, and eventually die off.

So, when testing for ammonia in the koi pond, it should read zero or less than 0.25 ppm.

If ammonia is testing at high levels in your koi pond, it is best to do a minimum of 10% water change, as this will remove a big chunk of the ammonia problem while providing the koi with clean water. 

Ensuring your filtration system is adequate for the number of koi fish in your pond is another important item you assess. If your biofiltration system is not up to par with the number of koi in your pond and the amount of food you are feeding them, you will always have an issue. There are water additives sold that can lower the ammonia by binding to it. However, the ammonia is still in the water, so you are not really removing it, just neutralizing it. My best advice is to do a water change for the benefit of the koi.

pH Levels

The ideal pH levels in a koi pond are between 7.0 to 8.6. Since you are performing water changes with your tap water, you should first test the pH level of the water source so you know exactly what you are adding to your koi pond. Remember if you are using city or municipal water, you may need to add a declorinator every time you do a water change.

The pH level of the pond water will affect your ammonia readings, meaning if you already have a high ammonia reading, a high pH level will cause it to become even more toxic for koi fish. High pH levels above 8.5 will affect you koi fish, look for the following signs: excess slime production, isolation, gasping at the pond surface, blood-streaked fins, resting on the bottom, and finally death. 

Performing a water change will be the best effect to lower the pH level of your koi pond. There are also some chemicals out there you can add to your pond to lower the pH, but fresh water is always best for the koi. If you add chemicals and it lowers the pH too fast, it can shock your koi. A water change will be more of a gradual lowering of the pH. Note that koi can survive a high pH longer than a low pH. Changing 10% of the water in your koi pond per day is the recommended and best solution to reducing high pH levels, in my opinion.

Nitrite Levels

Like ammonia, the nitrite levels in your koi pond should be zero. Symptoms of high nitrite in the koi pond are your koi will begin flashing (rubbing themselves on the bottom or walls of koi pond) or lay in the pond with fins clamped to sides of their bodies. Sometimes they will swim up to eat but then return to bottom of the pond and rest with fins clamped to sides.

If the nitrite level is high in the koi pond, perform a 25% water change. You can also add Bio start solution to your filter to boost the biofilter power. Test your water to make sure the nitrite levels stay within the range, reduce or stop feeding for a few days to also give the bio filter time to catch up and help lower the nitrites.

Nitrate Levels

Nitrate levels should be between 20 to 60 ppm in the koi pond. Nitrate levels above 80 ppm will require at least a 10% water change. Nitrate levels above 120 ppm is extremely toxic to koi!

In high nitrate conditions, koi may act dull or lethargic but perk up for feeding then quickly become lethargic again. High sludge in your pond can also cause high nitrate readings so besides performing a water change you can add a sludge remover to help keep levels in check.

GH & KH Levels

You should monitor the GH & KH levels in your koi pond periodically with a GH & KH test kit. KH levels can determine the possibility of pH swings. Ideal KH level is 105 ppm, plus or minus 15ppm.

Water Temperature

The best temperature range for koi is 65° to 75° F. It is best to avoid any temperature swings. Koi are cold water fish and can adapt to living in temperatures from 35° to 85° F, but the koi are not comfortable in those outer temperature levels. If your koi pond is not shaded and is shallow, such as 3’ or less, the water temperature in warm regions like the Central Valley or California, can rise quickly. Providing shade and deeper koi ponds will help maintain temperature levels, as well as doing more frequent water changes.

These are my thoughts and recommendations on helping everyone become better koi keepers, and providing your koi with the best water environment, so your koi are less stressed as well as their owners.

Happy koi keeping everyone!